So: why is the six week old embryo a potential human, but anyone reading this an actual human?

What's the difference between that embryo and you?

viability outside the womb.

take modern science into account and move the weeks of preg as "murder" vs removing a clump of cells. i,e, make abortion legal to the time prior to viability, and move that timeline back as science progresses.

Consider: June Wisenheimer is one month shy of her 100th birthday. Without any number of regular medical treatments and procedures, June will give up the ghost. Her days of biological viability are behind her. By your logic: we ought suspend any and all life-preserving -extending care and let her croak. Never mind that her mind is sharp, or that she might object to gettin' shoved into a grave.